1. Field of the Invention
The present invention relates to a neighbor node probing method which is a necessary process before transmission, and more particularly, to a method for probing a neighbor node using an adaptive and asynchronous rendezvous protocol, when a neighbor node is to be probed before communication is started in an opportunistic network in which the communication is performed only through intermittent connections, and a portable communication device using the same.
2. Description of the Related Art
Recently, much attention has been paid to new types of mobile ad-hoc networks such as opportunistic networks or cognitive networks. Such networks may be applied to various services such as military, vehicle, medical treatment, and multimedia transmission.
In an opportunistic network, nodes require link connection before transmission is started. However, since the mobilities or channel states of the nodes are changed minute by minute, the link connection may be maintained during a very short time.
For link connection, a node must probe a neighbor node within a transmission range thereof. In order to quickly probe a neighbor node, the node may continuously send a probing message. However, since most mobile nodes are operated by a battery, the operation of continuously sending a message requires large energy consumption. Therefore, the operation is almost impossible to be achieved in reality.
Therefore, a rendezvous protocol which is periodically woken up to probe a neighbor node is suitable for energy saving. When a neighbor node is to be probed within a given delay time, energy used for probing the neighbor node must be minimized. In general, as the energy used for probing a neighbor node increases, delay to discovery is reduced.
Furthermore, the rendezvous protocol for the opportunistic network must satisfy the following two conditions. That is, even when probing intervals between nodes are not synchronized (first condition) and even when wake-up patterns are different from each other (second condition), the nodes must be able to successfully probe neighbor nodes through the rendezvous protocol.
The rendezvous protocol operating in such an environment means that each of the nodes may independently perform probing using a wake-up pattern selected by remaining energy thereof or a required delay condition.
In order to satisfy such a request and solve such a problem, a variety of conventional techniques have been proposed. However, the techniques have some limitations in that they may not satisfy the above-described two conditions or may require an excessive number of probing messages or an excessively long probing period.
Representative examples of the conventional techniques may include QUORUM-based rendezvous protocols and DISCO-based rendezvous protocols. FIGS. 1A and 1B are diagrams for explaining QUORUM-based rendezvous protocols and a DISCO-based rendezvous protocol. FIG. 1A illustrates the basic idea of the QUORUM-based rendezvous protocols and the DISCO-based rendezvous protocol. FIG. 1B illustrates wake-patterns of the QUORUM-based rendezvous protocols and the DISCO-based rendezvous protocol on a time axis.
In FIG. 1A, suppose that the QUORUM-based rendezvous protocols share a predefined certain number (n). For example, suppose that all nodes share 4 (n=4).
At this time, one horizontal line and one vertical line are selected from a square table having a size of n×n. That is, one horizontal line and one vertical line are selected from a square table having a size of 4×4. Numbers displayed on the horizontal line and the vertical line selected in such a manner indicate slots which must be woken up. For example, when supposing that a third horizontal line and a fourth vertical line are selected from the 4×4 square table of FIG. 1A, the selected slots correspond to 8, 9, 10, and 11 in the horizontal line and 3, 7, 11, and 15 in the vertical line. That is, third, seventh, eighth, ninth, tenth, 11th, and 15th slots in FIG. 1B must maintain a wake-up and active state. Although different terminals randomly select one horizontal line and one vertical line from the square table having a size of n×n, the terminals have one or more common slots. That is, the different terminals may meet each other at the common slots.
The DISCO protocol is a protocol using the Chinese remainder theorem (CRT), and selects two prime numbers. Referring to FIG. 1A, prime numbers of 3 and 5 are selected, and terminals corresponding to multiples of the respective prime numbers maintain a wake-up and active state. That is, the multiples of 3 are 0, 3, 6, 9, and 12, and the multiples of 5 are 0, 5, and 10. Therefore, as illustrated in FIG. 1B, 0th, third, fifth, sixth, ninth, tenth, and 12th slots maintain a wave-up and active state. Therefore, although two different terminals start the rendezvous protocol at different time points, the DISCO protocol may also guarantee a rendezvous through the CTR.
However, the two rendezvous protocols have a limitation in that they require an excessive number of probing message or an excessively long probing period.